bug 1482159: Allow allow attribute for iframes
bug 1482159: Allow allow attribute for iframes

The allow value is a semicolon-separated list of restricted features to
allow an iframe to use. In Chrome and Safari, this is required for some
demos (such as those using the video camera) to run.  These browsers
still ask for the user's permission to use the feature.

a2sheppy/kuma,jwhitlock/kuma,Elchi3/kuma,mozilla/kuma,Elchi3/kuma,SphinxKnight/kuma,SphinxKnight/kuma,escattone/kuma,jwhitlock/kuma,jwhitlock/kuma,a2sheppy/kuma,mozilla/kuma,SphinxKnight/kuma,escattone/kuma,escattone/kuma,SphinxKnight/kuma,SphinxKnight/kuma,SphinxKnight/kuma,a2sheppy/kuma,Elchi3/kuma,Elchi3/kuma,mozilla/kuma,mozilla/kuma,mozilla/kuma,jwhitlock/kuma,a2sheppy/kuma,jwhitlock/kuma,a2sheppy/kuma,Elchi3/kuma